A variety of mechanisms have been shown to be responsible for the diversification of antibody repertoires in primary and secondary lymphoid tissues, a detailed knowledge of the differentiation and mechanisms responsible for the extensive and V region-focussed diversification (hyperdiversification) of rearranged immunoglobulin genes is not in hand. Somatic hyperdiversification of immunoglobulin V genes has been observed in several species including mice, rabbits, ruminants and chickens. In ruminants, the ileal Peyer's patch (IPP) is the site of primary diversification of the B cell repertoire. Very large members of B cells (1X10/10 - 1X10/11) undergo developmentally regulated, extensive somatic diversification of Ig genes. Although the ready availability of a tissue that is the site of such massive B cell diversification make it an attractive system for the detailed examination of the mechanism responsible for this process, precise knowledge of the kinetics of its onset are lacking. Furthermore, the relationship in time between the generation of diversity in the Ipp and the time when a diversified repertoire appears in the periphery is not known. Experiments are proposed that will employ RT-PCR nd single strand conformational polymorphism (SSCP) as an assay of somatic diversification of the lambda light chain V regions of cattle. The proposal has the following specific aims: 1. Determination of the point in development when bovine light chain V regions undergo diversification in ileal Peyer's patches. 2. Determine when the diversification in ileal Peyer's patches is reflected in the periphery. These studies will allow determination of the time in development when the diversification mechanism of IPP is activated and increases in activity. Such information is a necessary prelude to the informed undertaking of an examination of the factors that are involved in the initiation of an immunoglobulin diversification program in this site of B cell development and diversification.